arm64: kernel: Prepare for a DISR user

KVM would like to consume any pending SError (or RAS error) after guest
exit. Today it has to unmask SError and use dsb+isb to synchronise the
CPU. With the RAS extensions we can use ESB to synchronise any pending
SError.

Add the necessary macros to allow DISR to be read and converted to an
ESR.

We clear the DISR register when we enable the RAS cpufeature, and the
kernel has not executed any ESB instructions. Any value we find in DISR
must have belonged to firmware. Executing an ESB instruction is the
only way to update DISR, so we can expect firmware to have handled
any deferred SError. By the same logic we clear DISR in the idle path.

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 116a5c9443a7..5612d6f46331 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1039,6 +1039,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		.sign = FTR_UNSIGNED,
 		.field_pos = ID_AA64PFR0_RAS_SHIFT,
 		.min_field_value = ID_AA64PFR0_RAS_V1,
+		.enable = cpu_clear_disr,
 	},
 #endif /* CONFIG_ARM64_RAS_EXTN */
 	{},
@@ -1470,3 +1471,11 @@ static int __init enable_mrs_emulation(void)
 }
 
 core_initcall(enable_mrs_emulation);
+
+int cpu_clear_disr(void *__unused)
+{
+	/* Firmware may have left a deferred SError in this register. */
+	write_sysreg_s(0, SYS_DISR_EL1);
+
+	return 0;
+}